1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display including electron emission sources that use carbon nanotubes.
2. Description of the Related Art
The first field emission displays (FEDs) used Spindt-type electron emission sources, in which a material such as molybdenum or silicon is layered and formed to a sharp point at multiple locations. However, Spindt-type electron emission sources make manufacture complicated as a result of their microscopic configuration, and require highly precise manufacturing technology. These factors make application of Spindt-type electron emission sources to display devices of a large screen size difficult.
Therefore, there is an ongoing effort to simplify manufacture and make production of display devices having a large screen size easy by forming flat electron emission sources by using carbon-based materials.
Carbon-based materials suitable for forming electron emission sources include graphite, diamond-like carbon (DLC), and carbon nanotubes. Among these, carbon nanotubes appear to be very promising for use as electron emission sources. This is because carbon nanotubes have extremely minute tips with a radius of curvature of approximately tens to several tens of nanometers, and because carbon nanotubes are able to emit electrons while in a low electric field of about 1˜10V/μm.
Electron emission sources using carbon nanotubes are typically formed using a screen printing method. In the screen printing method, a paste mixture in which carbon nanotube powder, frit, and a vehicle are combined is screen-printed on cathode electrodes, then the mixture is heat treated to evaporate organic elements within the mixture. Next, the frit is fused such that carbon nanotubes are adhered to the cathode electrodes.
With the use of the screen printing method, manufacture is simple and application to large-screen display devices is possible. However, the electron emission sources formed using the screen printing method are such that most of the carbon nanotubes are embedded in solid granules of the paste and fail to protrude from a surface of the electron emission sources.
FIG. 15 shows a schematic view of an electron emission source formed using the screen printing method. Carbon nanotubes 3a and 3b are shown in detail. Although the carbon nanotubes 3a protrude from the surface of the conventional electron emission source 1, the carbon nanotubes 3b (i.e., most of the carbon nanotubes) are embedded in the solid granules. The carbon nanotubes 3b embedded in the solid granules are unable to perform electron emission. Reference numeral 5 in the drawing refers to a cathode electrode, reference numeral 7 to insulating layers, and reference numeral 9 to gate electrodes.
FIG. 16 is a scanning electron microscope photograph of an internal cross section of an electron emission source formed using the screen printing method. In the photograph, the spherical materials are solid granules. The thin carbon nanotubes are shown embedded within the solid granules.
Therefore, with the use of conventional electron emission sources using carbon nanotubes, the desired amount of electron emission for a certain level of the electric field generated in the peripheries of the electron emission sources is not obtained. To realize the desired level of electron emission, a higher voltage must be applied, that is, a higher overall drive voltage is needed. In addition to the greater power consumed, the application of a high voltage results in a reduction in the lifespan of the electron emission sources.